Clean room having substantially vertical air flow therein



Jan. 6, H970 W. B. WOOD 3Afi7fifi CLEAN ROOM HAVING SUBSTANIIALLYVERTICAL AIR FLOW THEREIN Filed Jan. 12, 1968 f2 /4 .f, I @J m W W I kwI EH-=- E; H6. 2 20 INVENTOR. MWU'ER EMUGE W000 (1 and 1W L fl/S UnitedStates Patent 3,487,766 CLEAN ROOM HAVING SUBSTANTIALLY VERTICAL AIRFLOW THEREIN Walter Bruce Wood, Bridgeville, Pa., assignor, by mesneassignments, to American Air Filter Company, Inc., a corporation ofDelaware Filed Jan. 12, 1968, Ser. No. 697,362

Int. Cl. F24f 7/06, 13/06 US. Cl. 98-31 11 Claims ABSTRACT OF THEDISCLOSURE A clean room is provided having a substantially vertical airflow from the ceiling down to a perforated floor which overlies a seriesof vertical chambers. The chambers act to direct air in a verticaldirection and counter horizontal air flow or other turbulences whichotherwise tend to disturb the air flow.

Background of the invention It has become the practice in a number oftechnological areas such as, for example, electronics and spacetechnology to provide so-called clean rooms in which precisionequipment, components, and the like can be assembled in an atmospherehaving minimum amounts of impurities such as airborne dust, dirt and thelike. Such a clean room normally has filtered, purified air admittedinto the room from the ceiling and withdrawn from the room at the floorto remove any dirt, etc. This downward flow also acts to prevent dirt,which may be on the floor, from contaminating materials in the room bybeing conveyed ofl? the floor onto the material which condition mightwell occur if the air flow was other than downward. Ideally, therefore,the air should enter the room via regularly spaced intervals throughoutthe entire ceiling and then pass directly down to corresponding openingsin the floor so that the air flow is entirely vertical and no crosscurrents or turbulences are built up which would tend to allowcontamination generated from any internal source to be transmitted in ahorizontal plane throughout the room.

However, the usual practice is to connect the openings in the floor to acommon duct which, in turn, feeds the air into a circulating pump whichpurifies the air and circulates it back to the room via the ceiling.This has created problems because the openings in the floor do notnormally draw equally from the various portions of the room. To overcomethis, elaborate battling systems have been used. However, even suchbaflling systems are still easily unbalanced by persons moving about theroom, repositioning of furniture and the like.

This unbalancing and unequal drawing of air can be easily explained interms of venturi effect created at each opening from the room into theduct. As the air is collected in the farthest corner of the room (withrespect to the circulating fan) it rushes through the duct beneathother, closer, openings and a suction or venturi effect is createddrawing excessive amounts of air through the closer openings which, inturn, is usually compensated for by bathing or the like. Therefore, theamount of air passing through a given opening in the floor is dependentupon the amount of air passing through the other openings in the floor,particularly upon those other openings which are spaced a furtherdistance from the circulating fan. Repositioning of furniture such asmovement of a chair or the like, as well as movement of personnel in theroom, can cause temporary starvation of air fiow through any one openingor group of openings in the floor which can cause unbalance in thesystem thereby causing horizontal, or at least nonvertical air currentsto be generated.

Quite surprisingly, it has now been found that a clean room can beconstructed which will provide substantially vertical and possibly acolumnar or laminar air flow in the room.

Summary of the invention -In accordance with the invention, a system forvertically directing air flow in a clean room comprises an enclosedspace having a wall with a ceiling portion and a fioor portion and meansfor circulating the air downwardly into the enclosed space from theceiling and means in the floor portion for controlling the direction offlow of the air in the enclosed space and for removing the air from thespace. The means for controlling the direction of flow of the aircomprise a plurality of parallel vertical chambers. The chambersinterconnect between a series of openings in the floor leading from theenclosed space into the chambers and a second series of openings at theopposite end of each chamber leading into a collection duct. The air canbe recirculated from the collection duct back into the enclosed spacethrough the ceiling by suitable means.

Brief description of the drawings FIGURE 1 is a cross-sectionalschematic view of a clean room using the invention.

FIGURE 2 is an isometric partially broken away view of a lower corner ofthe clean room and the vertical chambers beneath the floor.

FIGURE 3 is a cross-sectional portion of FIGURE 1 along lines 3-3showing the chambers.

Detailed description As previously stated, the invention provides asubstantially vertical downward air flow of air in a clean room.Referring now to FIGURE 1, a clean room is generally indicated at 2comprising an enclosed space 4, an air collection assembly 6 comprisingthe floor of the clean room, and a collection duct 8 beneath collectionassembly 6 which collects the air from the assembly and passes it tocirculating and filtering means 10. This can be any suitable fan andfiltering means or the like including means for controlling temperature,humidity and the like such as are Well known in the art. The clean airthen passes through duct 12 into duct 14 which is located above ceiling16. Ceiling 16 is provided with regularly spaced openings (not shown) toadmit the air downwardly in a vertical direction into enclosed space 4.Ceiling 16 can be any conventional porous: ceiling such as is well knownin the art.

Now referring to FIGURE 2, the collection assembly generally indicatedat 6 comprises a perforated upper plate 20 having spaced perforations 22therein, a plurality of vertical chambers 24 and a lower perforatedplate 26 having spaced perforations 28 therein. As best seen in FIGURE3, each chamber 24 is sealed with respect to adjacent chambers, butcommunicates respectively through perforations 22 and 28 with enclosedspaced 4 and collection duct 8. Preferably, the perforated openings, inboth top plate 20 and lower plate 26 comprise about 550 of the totalarea of the plates overlying the chambers. The size of each opening isnot critical. However, the size should be uniform and preferably thesame for both plates. The area of the opening should also be smallerthan the cross-sectional area of the chamber. In this way, a pressuredifferential between enclosed area 4 and chambers 24 is created acrossupper plate 20; and a second pressure differential is created in likemanner between chambers 24 and collection duct 8 across lower plate 26.Thus, the chambers 24 are maintained at a pressure intermediate to therespective pressures in enclosed space 4 and collection duct 8. Thechambers 24 cause the flow of air entering the enclosed space 4 throughceiling 16 to pass substantially vertically downward through openings 22in plate 20 into chambers 24.

While the mechanism by which chamber 24 accomplishes this columnar flowis not entirely understood, it is thought that each chamber functions asa cushioning device or surge tank resisting changes in the pressuredifferential which exist respectively between space 4 and chambers 24,and chambers 24 and collection duct 8. Thus, temporary inbalancescreated by movements of persons or objects, which might otherwise starveair flow through certain openings by redirecting the vertical flow toother openings, are resisted, or compensated for, by the chambers aswell as each chamber tending to provide the same output of air to duct 8despite temporary starvation or reduction of air output flow into thechamber caused by movement. This constant output, in turn, preventsmovement in the room or transient air currents from causing completeinbalance of the entire system such as occurred in prior constructionswhere interruption of air flow at any one opening into the duct could,in turn, effect the pattern of air flow into each and every otheropening into the duct causing a change in the drawing power of the ductat any given opening.

It should be noted here that the venturi effect previously discussed issubstantially eliminated or at least nullified in accordance with theinvention without any conventional dampening devices employed in thefloor system.

For example, a clean room 12' x 24 was constructed in accordance withthe invention. The entire floor was made as shown in FIGURE 2 by using a6 thick honeycomb kraft paperboard construction wherein each honeycombchamber was hexagonal and had a cross-sectional area of about 0.65square inch. The top and bottom of the honeycomb kraft paperboard wascovered with 24 ga. perforated steel plates having A5" uniformly spacedperforations on /4" centers. A conventional porous ceiling was used toadmit air into the room and the air was collected from the chambers in alower duct such as that previously described. Various air flowvelocities ranging from 30-120 feet per minute were tested, and smokepatterns in the room indicated that the flow of air remained verticaland uniform through the room.

The novel construction of the invention offers additional advantages tothose engineering the construction of such room because the structuralsupport which the construction offers far exceeds that of a singleperforated sheet which must be supported at closed intervals or elsemade thicker thereby increasing the cost. It has been found, forexample, that rooms made in accordance with the invention using 24 gaugesteel plates separated by chambers having kraft paper walls can easilywithstand loadings of 200-300 pounds per square foot with little if anydeformation'even when supported on 24-inch centers.

It is to be understood that neither particular crosssectional shape ofthe chamber nor the material from which it is constructed is critical.The cross-sectional shape could be circular or polygonal or the like. Itcan be constructed of sheet metal, plastic, kraft paperboard or othersuitable materials. The length of the chamber can be varied as well.However, it has been found that the minimum length of the chamber mustbe at least 4 times the diameter or longitudinal measurement of theopening to provide a suflicient capacity in the chamber relative to thepressure differential across the opening. Likewise, the collectionassembly 6 need not occupy the entire floor area of the clean room;modules of collection assemblies can be regularly spaced throughout theroom. However, since the invention provides a means for obtainingsubstantially vertical air flow in a room it is advantageous to spacethe modules as close together as possible.

It should be noted that the air need not enter solely through theceiling, but may enter as well through the ducts placed in the wall nearthe ceiling. However, for maximum utilization of the vertical aircurrent flow made possible by this invention, the entrance ducts shouldbe placed in the ceiling and should be placed as uniformly as possiblethroughout the entire ceiling.

Although the novel system of the invention has been illustrated in aparticular embodiment wherein a single layer of vertical chambers isused, it is to be understood that the invention contemplates the use ofone or more layers of vertical chambers separated by perforated platesto cause pressure differentials between the layers of chambers as well.

While the system described is preferably utilized to direct air flowvertically and smoothly into a perforated floor, it is recognized thatthe system could also be used in the ceiling to more uniformlydistribute air into a room. The invention is, therefore, to be limitedonly by the following claims.

What is claimed is:

1. A controlled environment enclosure having:

(1) a porous ceiling through which air is downwardly directed into saidenclosure; and

(2) a porous floor comprising a plurality of longitudinally extendingcolumnar vertical chambers, said chambers being of substantially uniformcross section along their longitudinal axis and in parallelrelationship, each being sealed with respect to adjacent chambers andhaving an upper portion with at least one opening therein in directcommunication with said enclosure and a lower portion with at least oneopening therein opposed to the opening in said upper portion andcommunicating directly with an air collection duct, the respective areasof the openings in said upper portions and said lower portions beingeach less than the cross-sectional area of said chamber, saidlongitudinally extending columnar vertical chambers acting to direct theflow of air in said enclosure from said porous ceiling downwardly in asubstantially nondeviating vertical direction to said chambers.

2. The enclosure of claim 1 wherein the length of said chamber is atleast four times the diameter of said open ing into the chamber.

3. The enclosure of claim 1 wherein said porous floor comprises an upperportion which is a perforated metal plate, a spaced lower portion whichis a perforated metal plate and a series of vertical chamberstherebetween of corrugated material having an upper edge sealed to saidupper perforated metal plate and a lower edge sealed to said lowerperforated metal plate to prevent the chambers from communicating withone another and to provide physical support beneath said upperperforated plate to mitigate buckling of said upper plate beneath aload.

4. The enclosure of claim 3 wherein said porous floor comprisesperforated steel plates having corrugated kraft paperboard therebetween.

5. The enclosure of claim 4 wherein said steel plates having circularopenings therein of about Ms" diameter spaced apart on about centers,and said corrugated kraft paperboard forms hexagonal chambers of about 6inches in length and a cross-sectional area of about 0.65 square inch.

6. A system for vertically directing air flow in a clean room comprisinga space formed by:

awall;

a ceiling; and

means spaced above said floor portion for admitting .air downwardly intosaid space;

means in said floor portion for causing the air to flow substantiallyvertical in said space and for removing air from said space, said meanscomprising a plurality of regularly spaced longitudinally extendingcolumnar vertical chambers, each having spaced opposed openings, one ofwhich openings communicates directly with said space, each of saidchambers being of substantially uniform cross section along itslongitudinal axis, said chambers being sealed from each other andforming zones of intermediate pressure between said space and acollection duct beneath said chambers.

7. The system of claim 6 wherein said means for admitting air comprise aporous ceiling and said means in said floor portion are spaced atregular intervals throughout said floor.

8. The system of claim 6 wherein said means in said floor coversubstantially the entire floor area.

9. The system of claim 6 wherein said floor portion comprises aperforated metal plate having openings therein communicating with theupper ends of said chambers and a second perforated metal plate belowsaid chambers and having openings forming exit openings from saidchambers to a collection duct, said openings forming pressuredifferentials to maintain said chambers of a 6 pressure intermediate tosaid space and said collection duct.

10. The system of claim 9 wherein said vertical chambers have a lengthat least 4 times the diameter of the openings into said chambers.

11. The system of claim 10 wherein said openings in said perforatedmetal plates comprise 550% of the total area of said plates.

References Cited UNITED STATES PATENTS 2,912,918 11/1959 Mead.

3,148,676 9/1964 Truog et a1. 126-246 3,158,457 11/1964 Whitfield.

3,314,353 4/1967 Knab 9831 FOREIGN PATENTS 1,162,473 4/1958 France.

LLOYD L. KING, Primary Examiner U.S. CI. X.R. 983 3

